This invention relates to the field of twisting technology in general and more particularly the layer-wise SZ twisting of twisting elements of electric cables in which the resulting twist is produced by means of a twisting plate with alternating direction of rotation.
Past development in the field of SZ twisting technology has led to twisting machines with which two to five twisting elements can be twisted with each other without problem. Further development in this field consequently has as an objective, among others, to also be able to twist a larger number of twisting elements with each other. This should be done within the scope of layer-wise SZ twisting.
For the layer-wise SZ twisting of twisting elements of electric cables, a twisting machine is already known which consists essentially of a customary SZ twisting portion with two twisting heads arranged respectively at the beginning and at the end of a taut twisting accummulator. The alternating rotary motion of the twisting heads is arranged so that, when the twisting elements enter the twisting machine, the lengths drawn in, on the average, are exactly those which are required in the finished twisted assembly (DE-OS No. 27 26 172). Such a twisting device is well suited for the twisting of 1+6+12 twisting elements. Applying further twisting layers however, presents difficulties because of twist reversal processes which occur. This as also true for another known twisting device which contains a separate twisting closer followed by a twisting head, for each twisting layer and in which the individual twisting heads, together with a twisting head common to all twisting layers forms several taut, interleaved twisting accummulators. The distances and speeds of rotation of the twisting heads in this device are matched to each other in a particular way (DE-OS No. 28 28 959). Particular difficulties arise in controlling the length differences of the twisting elements which occur in twist reversal processes.
For SZ twisting of 4 to 5 twisting elements another twisting device is known which contains a twisting plate, rotating with alternating direction of rotation, as the twisting tool and in which the twisting head can be arranged at a certain distance from the twisting plate immediately behind a twisting closer. The twisting head revolves with the same direction of rotation as the twisting plate but only at half the speed (DE-OS No. 24 54 777). In another known twisting device of this kind, the twisting head runs only intermittently (French Provisional Patent No. 2,403,633). SZ layer twisting of twisting elements of electric cables can also be carried out with a twisting plate, the guide holes of which are arranged on two pitch circles and which isprovided with tubular accummulators for the twisting elements of different twisting layers (DE-OS No. 26 15 275). Instead of tubular accumulators, several twisting plates can also be provided (U.S. Pat. No. 3,187,495).